Western Flycatcher

The Western Flycatcher was formerly split into two species, Cordilleran and Pacific-slope Flycatcher. After a comprehensive systematic study of geographic variation characterizing differences in size and colour, vocalizations, genetics and ecology, in 2023, ornithologists lumped Pacific-slope and Cordilleran Flycatchers together as Western Flycatcher after treating them as separate species since 1989. It breeds from southern Alaska south along the Pacific Coast to northern Baja California. It extends inland as far as western Alberta and winters in Baja, Mexico and along the western Mexican coast.

Adult Male (spring/summer)

Head greenish-gray with prominent pale yellowish eye ring and lores and, a slight crest. Chin is grayish-white; breast is olive-brown; belly, flanks and undertail coverts pale yellow. Back, rump and uppertail coverts dark olive-brown. Wings are charcoal-olive with two prominent wing bars and white feather edges. Tail is charcoal-olive. Upper mandible is dark and lower flesh coloured.

Adult Female (spring/summer)

Similar to adult male.

Juvenile:

Similar to adults but wing bars are buffy.

General:

Small Empidonax flycatcher. Length: 14-17cm. Wing: 20-23cm. Weight: 8-12grams.

Behaviour:

Like many flycatchers, this passerine sits on inconspicuous branches and hawks for flying insects. Sometimes it will glean prey off leaves. Shallow wing-beats give it a weak-fluttering flight. It is almost exclusively insectivorous but it has been observed feeding on berries and seeds.

Habitat:

Found in moist deciduous woodlands or moist mixed forests that provide sufficient shade. Riparian woodlands provide the best breeding habitat.

Information:

Pacific-Slope flycatchers winter in Mexico and Central America and return to the western US and Canada during the breeding season. Breeding females tend to build near water in a tree crotch, on cliff ledges and sometimes human structures. They prefer shady areas and the nest will be between 0.3 m to 13 m above ground. Nest is large and bulky consisting of moss, lichen, grass, and twigs and lined with finer material such as fur and feathers. The clutch is 3-5 eggs. Sometimes a second brood is reared. First brood fledges in May and the pair may nest again in July. There is a low incidence of brood parasitism by cowbirds.

Similar species:

Cordilleran Flycatcher.

Conservation Status:

Listed as Least Concern. Population is stable or slightly declining.

Capture Rates:

As a migrant species, capture of Pacific-slope Flycatcher occurs starting in April and continues through October. Capture rate (2010-2012; standardized as birds captured per 100 net hours) peaks substantially in August corresponding with dispersing juveniles and adults using Colony Farms as a foraging area before they continue their southern migration to the wintering grounds in Central America.

Molt Summary:

PF: partial; PB: AHY complete
Preformative molt includes 1-5 inner gr covs and sometimes includes 1-3 terts (rarely s6 as well)
1st PAs include 0-5 inner gr covs, often 1-3 terts, and rarely 1-2 central rects
Adult PAs include 0-3 inner gr covs, sometimes 1-3 terts, and occasionally 1-2 central rects (r1)

Pacific-slope Flycatcher from other Empidonax Flycatchers

A good way to start is to divide Empids in to 3 main groups:

White throat, white belly and spotted crown – Traill’s (Willow/Alder) and Least
Greyish throat, yellowy belly and narrow bill – Hammond’s and Dusky
Yellow throat, yellow belly and greenish back – Pacific-slope and Yellow-bellied

Throat – Yellow / Belly – Yellow / Back – Greenish / P6 – Emarginated / Primary projection – medium with one long gap / Bill – Wide, sides convex / Lower mandible – Yellow/orange / Appearance – Often semi-crested / Eye-ring – almond shaped / Legs – Grey legs unique

Often semi-crested / Grey legs unique

Primary projection medium: 10-17mm P6 – P5 one long gap

This SY in May is showing 3 generations of feathers: GCs 7-10 and the 3 tertials (blue arrows) which are first alternate feathers i.e. the most recently molted feathers from the prealternate molt this spring; GCs 2-6 which are formative feathers i.e. retained feathers from the preformative molt last fall; and finally, the outermost greater covert (GC1), carpal covert, two main lower alula feathers, primary coverts, primaries and secondaries which are all retained juvenal feathers.

Notice also the narrow, tapered and worn primary coverts and wear to the tips of the remiges (primaries and secondaries).

The rectrices of the above SY in May are showing extreme wear to the tips. The deficiency of pigmentation in these retained juvenal tail feathers cause the tail to appear almost transparent and also notice the very pale brown rachises.

Feather exposure to sun and abrasion is the major cause of feather deterioration and is especially hard on juvenal feathers. Exposure wears down feathers both through structural weakening and break-down as a result of solar irradiation, and through physical abrasion against foliage and the ground. Because juvenal feathers are of poor quality, they tend to wear down and fade more rapidly than subsequently grown feathers.

This SY also in May also has 3 generations of feathers but this photo illustrates how replacement of feathers in molt is not always sequential especially in Empids.

GC 2 (red arrow) is likely a retained juvenal feather; GC 6 (blue arrow) is likely a first alternate feather with the remaining GCs likely being formative feathers. The innermost secondary S6 (red arrow) is a formative feather and all 3 tertials first alternate feathers. The carpal covert, primary coverts and remaining remiges are all retained juvenal feathers although it is difficult to discern whether the 2 innermost primary coverts were also replaced feathers in the preformative molt.

The rectrices of the bird immediately above are relatively narrow and lightly pigmented again with very pale brown rachises although with less wear than the SY at the top of the page.

Another second year (SY) bird in June showing 3 generations of feathers; formative lesser, median and greater coverts, carpal covert, alula covert (A1); first alternate inner greater coverts, and all 3 tertial (S7-S9); and retained juvenile primaries, secondaries, primary coverts and lower alula feathers (A2 & A3).

The rectrices of the bird immediately above are relatively narrow and lightly pigmented again with very pale brown rachises although again with less wear than the SY at the top of the page.